Up to now, optical scanning apparatuses that can increase a practical scanning speed of a laser beam have been known (see, for example, PTL 1). An optical scanning apparatus described in PTL 1 includes: a beam splitter that reflects a laser beam, allows the laser beam to be transmitted therethrough, and branches the laser beam into a plurality of light fluxes; a half mirror that reflects the laser beams transmitted through the beam splitter; a scanner that applies for scanning the laser beams that are reflected on the beam splitter and the half mirror at different exit angles and are gathered on the same point; and a diaphragm that selectively allows the laser beams applied for scanning by the scanner to pass therethrough.
In the optical scanning apparatus described in PTL 1, the laser beams reflected on the beam splitter and the half mirror are simultaneously applied for scanning by the scanner, and only any of the laser beams is sequentially allowed to pass through the diaphragm. Consequently, during one swing of the scanner, the plurality of laser beams are sequentially applied for scanning while the irradiation range is shifted, so that the time required to scan a given area is shortened.